Percussion tool

ABSTRACT

This disclosure relates to a percussion tool which includes a housing having a chamber reciprocally mounting a piston with first and second pressure ducts at opposite ends of the latter and a control duct therebetween as well as a return duct in fluid communication with the chamber at a point intermediate the points of entry of the first and second pressure ducts, the improvement includes movable valve means in the form of an annular open ended valve sleeve operative for alternately placing the inlet and pressure ducts in fluid communication in a first position and placing the first pressure and return ducts in fluid communication in a second position while at the same time maintaining fluid communication between the inlet and second pressure ducts and closing communication between the inlet and first pressure ducts. The valve sleeve includes both an annular collar and a circumferential groove associated with selected ones of the latter-mentioned ducts for imparting the reciprocal motion to the valve sleeve.

United States Patent Klemm PERCUSSION TOOL Inventor: Gunter Klemm, Olpe, Germany Assignee: Fa. Ingenieur Gunter Klemm Spezialunternehmen fur Bohrtechnik. Olpe, Germany Primary E.\'aminer.lames A. Leppink Attorney, Agent, or Firm-Diller, Brown, Ramik &

Wight 1451 Sept. 30, 1975 5 7 ABSTRACT This disclosure relates to a percussion tool which includes a housing having a chamber reciprocally mounting a piston with first and second pressure ducts at opposite ends of the latter and a control duct therebetween as well as a return duct in fluid communication with the chamber at a point intermediate the points of entry of the first and second pressure ducts, the improvement includes movable valve means in the form of an annular open ended valve sleeve operative for alternately placing the inlet and pressure ducts in fluid communication in a first position and placing the first pressure and return ducts in fluid communication in a second position while at the same time maintaining fluid communication between the inlet and second pressure ducts and closing communication between the inlet and first pressure ducts. The valve sleeve includes both an annular collar and a circumferential groove associated with selected ones of the lattermentioned ducts for imparting the reciprocal motion to the valve sleeve.

20 Claims, 2 Drawing Figures US. Patent Sept. 30,1975

Sheet 1 of 2 U.S. Patent Sept. 30,1975 Sheet2of2 3,908,767

PERCUSSION TOOL This invention relates to a percussion tool having a reciprocally mounted working piston hydraulically movable in a working cylinder or bore which, depending on the position of the working piston, connects alternately various ones of pressure lines or ducts, return lines or ducts, control lines or ducts, for controlling'the operation of the working piston.

In known percussion tools a control valve or piston is generally rather massive in size and has sections of different diameters which is movable in a bore or cylinder sub-divided into a plurality of individual chambers. Depending upon the position of the control valve different chambers of the control bore or cylinder are sealed off from each other or connected to each other so that various ducts i.e., pressure duct, inlet'duct, re turn duct, control duct, etc., are alternatively sealed off from each other or connected with each other so that with varying combinations of the latter the working piston is controlled in its operation.

It is known to operate the control valve in such a way that one of its axial terminal surfaces or faces is always exposed to full inlet hydraulic pressure while its axially opposite face is at times out off from the ductor line conducting the hydraulic pressure by means of the working piston. In such case the working piston normally has two shelves or casing surfaces which are in sealing engagement against the bore or cylinder surface of the working cylinder. A control duct between the surfaces is in fluid communication with the control valve for controlling the operation of the working piston.

In another percussion device another massively constructed control valve is continually exposed at one side to high pressure and several ducts lead from various points from the working cylinder or chamber into a chamber containing the control valve. The control valve consists of two valve parts connected to each other which connect the control ducts alternately with each other or with the high pressure line or the return line. The control valve is likewise disposed in a cylinder or bore which has aa complicated system of annular grooves or chambers and connecting ducts.

Finally, in the case of another known percussion tool the control valve or piston is constructed in three parts having longitudinal bores which bridge the individual parts of the valve. In this tool the shape of the control valve as well as that of the bore within which it is movably mounted is relatively complicated.

The latter defined conventional percussion tools in which the control valves are of massive construction or have small longitudinal bores have the disadvantage of being of a complicated construction due to the intricate machining of the valves and the bores, but an addition disadvantage is the fact that the control valve must be of a relatively heavy construction. With the large number of impacts necessary in modern percussion tools (50 impacts per second) a large mass means high inertia and therefore strong mechanical stress on the impact of the walls of the bore of the control valve. This produces a great amount of wear and in practice has shown that massive control valves can actually be driven through the walls of the bore or cylinder housing the same.

It is also known to employ a valve formed as an annula r sleeve which is arranged in a bore having formed cation of the valve sleeve is relatively small and theretherein a concentrically arranged groove. However, in this case a duct which is opened and closed by reciprofore there is a great resistance to flow precluding large amounts of working fluid to be operative through the system, particularly into the working cylinder or chamber, in a relatively short period of time.

In view of the foregoing, it is a' primary object of this invention to provide a percussion tool of the type mentioned although in the present instance the control valve is of a simple and uncomplicated construction, as a low mass inertia, and is operative to permit a high rate of flow when the valve is open. The control valve is an annular hollow valve or valve sleeve with a free internal space which at one of its sides adjacent and end can close off a pressure duct leading to the working cylinder or bore. This construction permits the control valve to permit a large amount of flow of the hydraulic or other fluid media involved at low mass inertia. The low mass inertia is created due to the fact that the wall thickness of the annular valve sleeve is simply thick enough to withstand operating pressures of the fluid media but apart from that it includes a cylindrical bore which advantageously, also allows the use, at least in one embodiment of the invention, of a return spring for operating the valve sleeve.

In keeping with a further object of this invention two pressure ducts lead from the working cylinder or bore to axially opposite ends of a bore or chamber housing the valve sleeve and pressure is impinged against axially opposite annular faces of the valve sleeve which faces are of different areas to control the operation of the valve .sleeve depending upon the various pressures in the two pressure lines. A control duct from the working bore or cylinder enters the control valve bore intermediate the points of entry of the two pressure ducts and auguments the reciprocal motion of the valve sleeve depending upon the pressures exerted against the axially opposite terminal end faces of the valve sleeve by the latter mentioned two pressure ducts. By this construction the operation of the valve sleeve is totally automatic and conventional manual mechanical resetting of various elements areavoided.

In further keeping with another object of this invention a larger of the terminal endfaces of the valve sleeve as grooves or indentations which oppose a seat with a spring normally biasing the indentations away from the seat such that pressure prevailing in one of the pressure ducts will in every case act upon the grooved face of the valve sleeve and tend to lift the same in a direction away from the seat thereof.

A further object of this invention is that of regulating the point of reversal of the reciprocation of the valve sleeve. In conventional percussion tools of the type described a control duct leading from the working cylinder or bore includes several branch ducts which subsequently join into a single control duct. The branch ducts, which are arranged in staggered relationship, can be closed or opened by the reciprocal motion of the control piston (not the working piston). Thus by opening-the individual branch ducts under the reciprocation of the control piston the upper reversing point of the working piston at each stroke can be determined which results in a reversal of motion of the latter. The precise point of reversal of the working piston is necessary for an efficient conversion of hydraulic energy into percussion energy. However, in such construction the point of reversals causes the control valve to jerk in its movement bringing about a sudden pressure reversal upon the working piston which produces corresponding reaction forces (.jerking) on the working piston.

Thus both the control valve and theworking piston. as well as the bores or cylinders thereor, are subjected to a high load on the terminal of the return stroke. However, in keeping with this invention the return stroke of the working piston reaches its final position in the absence of such jerks due to the use of one or more adjustable throttle elements which alter the flow as desired to produce a steady decline in speed of the working piston.

In keeping with the latter described object, the control duct includes several branch ducts emerging out of the working bore or cylinder along the path of reciprocal travel of the working piston with each branch duct having a throttling element with the elements adjustable to achieve steady declining speed to the working piston toward its point of reversal. Preferably, though not necessarily, the latter is accomplished by arranging the throttling elements such that the flow of fluid from the working cylinder progressively increases in the direction of the return stroke of the working piston. This in effect starts the return stroke of the working piston slowly with an increase as another control branch duct is opened", more rapidly as a further control branch duct is open, etc.

In conventional percussion tools it is known to provide a hydropneumatic two-chamber pressure accumulator separated by a membrane with one of the chambers connected to the pressure duct of the percussion tool. A shut off valve is generally disposed between a duct leading to a chamber of the shut off valve into which also enters the inlet duct and a pressure duct. This shut off valve is operative when the pressure on the system drops below a predetermined value which is generally above the normal working pressure of the system. Though such shut-off valves are known, in keeping with the present invention a shut-off valve is provided which is operative only when the hydraulic pressure in the inlet duct is interrupted by the shutting down of the percussion tool which prevents entrapped high pressure from abruptly discharging into the pressure accumulator. The latter is undesired because the membrane heretofore described is slung or moved with great energy impact and in practice frequently breaks as a consequence thereof. The shut-off of this invention makes it possible to prevent this high energy motion of the membrane of the accumulator.

With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claimed subject matter, and the several views illustrated in the accompanying drawings.

IN THE DRAWINGS FIG. 1 is a cross-sectional view of a percussion tool constructed in accordance with this invention, and illustrates an annular hollow control valve or valve sleeve operative to control the flow of hydraulic fluid to a working piston reciprocally mounted in a working cylinder or bore.

FIG. 2 is a fragmentary sectional view through a modified construction of an annular control valve or valve sleeve, and through the construction thereof is operative in the absence of a biasing spring.

Referring first to FIG. 1, a percussion tool including a working cylinder or bore 10 within which is mounted for reciprocal motion a working piston 11. Upon the controlled rapid reciprocation of the piston 1 1 its lower end face (unnumbered strikes at intervals upon an anvil 12 which may, for example, be connected to a conventional drilling linkage.

A high pressure inlet duct or line 13 supplies a fluid medium, which is preferably hydraulic, under pump pressure of approximately bar to a pressure duct or line 15 and alternately to a pressure duct or line 19 through a shut-off valve 14 and a control valve 23, both of which valves are in the form of hollow annular sleeves. The pressure duct 15 is permanently connected to a lower chamber 16 of the bore 10 and to a lower portion (unnumbered) of a bore or cylinder 20 within which the valve sleeve 23 is reciprocally mounted so that pressure will act against a shoulder or annular surface 17 of the piston 11 which faces downwardly, as viewed in FIG. 1. This pressure from the pressure duct 15 acting against the annular surface 17 of the piston 11 tends to move the piston 11 in an upward direction.

An upper chamber 18 of the bore 10 is connected to the bore or cylinder 20 by the pressure duct 19 and depending upon the position of the valve sleeve 23 the duct 19 may be cut off in its communication with a return duct 21, as shown in FIG. 1, or may be placed in fluid communication therewith, as will be described more fully hereinafter, upon movement of the valve sleeve 23 to its upper most position thus the pressure duct 19 can be alternately connected to the pressure duct 15 and to the pressure duct 15 in conjunction with the return duct 21.

The piston 11 adjacent the upper chamber 18 includes an annular surface 22 facing axially upwardly, as viewed in FIG. 1, and the area of the surface 22 is substantially greater than the area of the surface 17. In the position of the elements illustrated in FIG. 1 like pressure will be directed by the ducts 15,19 into the chamber 16,18, respectively, to act against the annular faces or surfaces 17,18. By virtue of the smaller area of the surface 17, as compared to the surface 22, the piston 11 will be driven upwardly. Likewise if the pressure from the duct 15 acts only upon the surface 17, assuming that the duct 19 is closed, the piston 11 will also move in its return stroke in an upward direction.

The operation of the control valve or valve sleeve 23 is through a control duct 24 which includes a plurality of branched ducts 25 through 28 opening into the chamber 16 in axially spaced relationship along the reciprocal path of travel of the piston 11. The control duct 24 enters the bore or cylinder 20 at an annular portion 55 thereof such that fluid pressure impinges against an annular collar or surface 56 of the valve sleeve 23. Above the surface 56 of the valve sleeve 23 the latter is provided with a circumferential radially outwardly opening groove or recess 29 which is intermittenly placed into fluid communication with the pressure duct 19 and the return duct 21. When the valve sleeve 23 is in the position illustrated it will be noted that pressure is exerted upon an axial end face 30 of the valve sleeve 23, as well as upon an end face 33 of larger area opposite the end face 30. The end face 33 as a series of circumferentially disposed grooves or indentations 57 which oppose a seat 32 upon which rests the high side of the face 33. A spring 31 biases the valve sleeve downwardly while a spring 34 located conventionally by an element 35 normally biases the valve sleeve 23 upwardly. It is further pointed out that the total surface area of the surfaces 30,56 is identical to that of the surface area of the surface 33'.

As thus far described the operation of the percussion tool is as follows:

Beginning with the position of the parts as illustrated in FIG. 1 the valve sleeve 23 connects the duct 19 with the pressure duct and cuts off communication to the return duct 21. As full line pressure of the inlet duct 13 acts on the upper larger annular surface 22 of the piston 11 as well as on the lower smaller annular surface 17 of the piston 11 the piston 11 is accelerated in a downward direction. In doing so the piston closes off in sequence the branch ducts 25 through 28 from the lower chamber 16 which is under full line pressure. As the control duct 24 is finally completely cut off from inlet pressure of the inlet duct 13 the pressure in the control duct 24 becomes less than that of the pressure in the chamber 16 due to the reduction of its volume by the descent of the piston 11 whereupon the force acting against the face 56 of the valve sleeve 23 lessens as opposed to the force acting against the face 33 by virtue of the grooves or indentations 57 between the face 33 and the seat 32. The latter force and that offered by the spring 34 causes the valve sleeve 23 to move upwardly and once the total face 33 is exposed to full line pressure the spring 34 is ineffective and the valve 23 moves upwardly under only hydraulic pressure until it rises fully upwardly within the chamber or bore 20. In the latter position of the valve sleeve 23 the flow of fluid through the control sleeve 23 and the duct 19 into the chamber 18 is interrupted while at the same time the pressure duct 19 is connected through the circumferential groove 29 to the return duct 21. The upper chamber '18 therefore becomes pressureless by, for example, being vented to atmosphere so that the working piston 11 is now driven upwardly by virtue of the existing pressure within the chamber 16 acting against the surface 17 of the piston 11. During the upward motion of the piston 11 pressure flows from the chamber 16 through the branch ducts 25 through 28 into the control duct 24 and this force impinges against the surface 56 of the sleeve 23 causing the sleeve to descend from its upper most position to its lowermost position once again illustrated in FIG. 1. This increasing pressure in the control duct 24 is regulated by a plurality of throttle elements 36 through 38 which are of decreased thickness, as illustrated, such that as the branch duct 28 is exposed miminum pressure is exerted against the face 56 of the valve 23 and thereafter an increase in pressure is exerted against the face 56 by the progressive increase flow of fluid from the chamber 16 through the ducts 27,26, and 25, respectively. Because of this slow pressure build-up within the control duct 24 the control sleeve 23 in its downward movement moves gently and progressively so that there is not an abrupt impingement of full line inlet pressure through the duct 19 upon the surface 22 of the piston 11 which would result in a jerked motion of the latter. Therefore the working piston 11 is slowly and continually braked in its upward motion and does not in effect move against an incompressable hydraulic cushion within the chamber 18.

If the percussion tool thus far described is used in conjunction with drilling fixtures it may be provided with a flushing pipe 40 which passes longitudinally through a bore 41 of the working piston 11 as well as a'bore (unnumbered) of the anvil 12. The diameter of the bore 41 is greater than the exterior diameter of the flushing pipe 40 so that there is an annular air space between the two. The pipe 40 is fixed and the piston reciprocates relative thereto in the manner heretofore described and in so doing air is continually pumped into the cylinder 10 through the bore 41. This pro duces a cooling action internally of the piston 11 as well as within the bore 10 and also insures lubrication because the air contains leak oil in the form of mist. This oil and air admixture is therefore in effect pumped to all places where friction can arise to reduce wear of relatively moving parts within the bore 10. Moreover, an air cushion cannot be formed at axially opposite ends of the piston 11 and opposing portions of the bore 10 which would absorb the impact energy transmitted or desired to be transmitted by the piston 11 to the anvil 12.

The inlet duct 13 is also connected to a hydropneumatic pressure accumulator 43. which consists of a chamber containing gas under high pressure and a second chamber which is directly connected by a duct (unnumbered) to the inlet duct 13 or to the pressure duct 15. The two chambers of the accumulator 43 are separated from each other by a rubber membrane 44. The purpose of the pressure accumulator 43 is to absorb excessive pressure during the cycling of the tool particularly when only a little pressure is required whereas at times when higher pressure is required such can be made available from the accumulator 43. Through the use of an accumulator of this type the pressure from the pump associated with the inlet duct 13 need not meet the maximum value of the tool but only a mean value between high and low fuel requirements as the accumulator pressure could be used to augment the same.

' One difficulty of known pressure accumulators of the type described in which two chambers are separated by a membrane is that when the inlet duct 13 becomes pressure free the membrane 14 is slung or driven against the wall of the accumulator under high impact due to high pressure within the system resulting in fracture or breakage of the membrane. In actual practice such fracture arises when the pressure pump leading to the inlet 13 is switched off and entrapped high pressure within the system abruptly purges toward and into the accumulator 43 and against the membrane 44 thereof.

In order to avoid the latter-mentioned difficulties the shut-off valve 14 has been provided in the device and, like the control valve 23, is in the form of an annular valve or valve sleeve 45 having at its lower end a collar 46 and an axial end face 48 having grooves or indentations 49. A spring 47 normally biases the valve sleeve 45 in a downward direction and is so rated that the pressure acting upon the bottom face 48 normally drives the valve sleeve 45 upwardly. The valve sleeve 45 will move downwardly only when the pressure in the inlet duct 13 falls below, for example, bar and is no longer able to act against the spring 47. The normal pressure in the pressure accumulator under this example is approximately 50 bar.

In the open position of the valve sleeve 45 the inlet duct 13 is connected with the pressure accumulator 43 and with the pressure duct 15 through the interior of the valve sleeve 45. If the pressure in the pressure duct 15 falls below 70 bar then the valve sleeve 45 drops down and separates the three ducts 13,15 and the unnumbered duct from the accumulator 43 from each other. The pressure prevailing within the chamber cannot now be released abruptly into the accumulator 43 because the duct is closed off therefrom by the collar 46 of the valve sleeve 45. However, due to the indentations or grooves 49 the pressure within the chamber 16 will bleed slowly into the accumulator 43 and undesired impact forces against the membrane 44 is thus precluded.

The percussion tool also includes conventional seals 50 as well as leak ducts 51,52 which open into the return duct 21 to return any fluid which leaks pass the seals 50 or in a reduced central portion (unnumbered) of the piston 11.

Reference is now made to FIG. 2 of the drawing which illustrates an embodiment of the invention in which springs corresponding to those bearing reference numerals 31 and 34 in FIG. 1 are eliminated. In this case the valve sleeve 23' is slightly modified relative to the construction of the valve sleeve 23. The valve sleeve 23' has an annular or circumferential collar 56 having axially opposite faces, 30,33, the latter of which is of a greater surface area than the former. The collar 56 includes opposite incline faces 58,59 which are in respective communication with the ducts 24,21, with the latter being accomplished through a branch duct 60. Indentations 57 are also formed in the face 33 and these operate in conjunction with a seat 32 in the manner described relative to the valve 23.

The control of the valve sleeve 23' is exclusively hydraulic. The high pressure acts continually upon the larger surface area 33 and the smaller surface area 30. If the pressure in the control duct 24 is low then the force acting upon the face 33 becomes superior and the valve sleeve 23' is raised upwardly. If the pressure in the control duct 24 increases than the forces acting upon the faces 30 and 58 exceed that force which acts upon the face 33 and the control valve sleeve 23 moves downwardly. It is recognized that the pressure from the control duct 24 acting upon the rear face 58 of the collar 56 is exclusively decisive for the position of the control valve sleeve 23' at that time.

The advantage of the construction of the embodiment of the invention illustrated in FIG. 2 consists in that no type of spring or springs are necessary to produce a pretension or to lift the valve sleeve. The production is therefore simplified and wear of relatively moving parts is lessened. However, both as to the valve sleeves 23 and 23, each has the advantage that the adjustment movement thereof is introduced through a single duct, namely the control duct 24. The control duct 24 at the endentering the cylinder has no branches and enters the cylinder 20 at but one point. Thus the piston faces or surfaces of the control sleeves 23,23 are, with the exception of the face 58, always subjected to the same pressure whereby simple ducting is achieved and the number of controlled ducts from the working cylinder 10 to the control valve cylinder 20 is reduced simply to one.

While preferred forms and arrangement of parts have been shown in illustrating the invention, it is to be clearly understood that various changes in details and arrangement of parts may be made without departing from the scope and spirit of this disclosure.

I claim:

1. A percussion tool comprising a housing defining a chamber within which is reciprocally mounted a piston, first and second pressure ducts in fluid communication with said chamber at respective first and second sides thereof, a control duct in fluid communication with said chamber at said second side of said piston, a return duct in fluid communication with said chamber at a point intermediate the points of entry of said first and second pressure ducts relative to said chamber, an inlet duct for delivering a pressurized fluid to said pressure ducts, and movable valve means for alternately placing said inlet and pressure ducts in fluid communication in a first position of said valve means and placing said first pressure and return ducts in fluid communication in a second position of said valve means while at the same time maintaining fluid communication between said inlet and second pressure ducts and closing communication between said inlet and first pressure ducts, said valve means being an annular open ended valve sleeve mounted for reciprocal motion in a bore, said first and second pressure ducts open into said bore at axially opposite ends thereof, said return duct opens into said bore between the points of entry of said first and second pressure ducts relative to said bore, and said valve sleeve has first means on an outer peripheral surface thereof for placing said first pressure and return ducts in fluid communication in said second position.

2. The percussion tool as defined in claim 1 wherein said valve sleeve has second means on its outer peripheral surface for moving said valve sleeve from its first to its second position under the impingement of fluid thereagainst, and said control duct opens into said bore for so impinging fluid pressure upon said second means.

3. The percussion tool as defined in claim 1 wherein said valve means has an annular collar on its outer peripheral surface, said collar includes oppositely facing annular surfaces, said control duct opens into said bore for impinging pressurized fluid upon a first of said faces, a duct for placing said bore adjacent a second of said faces in fluid communication with said return duct, and the area of said first face is greater than the area of said second face.

4. The percussion tool as defined in claim 1 including spring means normally biasing said valve sleeve in a direction toward said second position.

5. The percussion tool as defined in claim 1 wherein said first means is a radially outwardly opening circumferential groove in said valve sleeve outer peripheral surface.

6. The percussion tool as defined in claim 1 wherein said valve means has an annular collar on its outer peripheral surface, said collar includes oppositely facing annular surfaces, said control duct opens into said bore for impinging pressurized fluid upon a first of said faces, a duct for placing said bore adjacent a second of said faces in fluid communication with said return duct, the area of said first face is greater than the area of said second face, said valve sleeve includes an annular terminal end force at anaxial end of said valve sleeve disposed adjacent said second pressure duct, said bore includes an annular seat against which abutts said terminal end face in said first position, and a plurality of grooves in said terminal end face whereby fluid pressure acting between said grooves and annular seat apply a force acting in a direction tending to move said valve sleeve from said first to said second position.

7. The percussion tool as defined in claim 1 wherein said piston has a pair of annular axially oppositely facing surfaces of differing surface areas, a larger of said annular surfaces being in fluid communication with said first pressure duct, and a smaller of said annular surfaces being in fluid communication with said second pressure duct.

8. The percussion tool as defined in claim 1 wherein said control duct enters said chamber in the area of said first pressure duct and more remote from said second pressure duct, adjustable throttle means for adjusting the rate of flow from said chamber through said control duct, and said control duct being connected to said return duct.

9. The percussion tool as defined in claim 1 wherein said control duct includes a plurality of branch ducts entering said chamber along axially spaced points in the area of said first pressure duct and more remote from said second pressure duct, the throw of said piston being sufficient to completely cover all of said branch ducts and progressively open the same, adjustable throttle means for adjusting the rate of flow from said chamber through said control duct branches, and said control duct remote from the branches thereof being connected to said return duct.

10. The percussion tool as defined in claim 1 including a bore in said piston, a flusing pipe disposed in said bore and being attached to said cylinder, and an annular gap between said bore and flashing pipe.

11. The percussion tool as defined in claim 1 including a control valve between said inlet and second pressure ducts, an accumulator, an accumulator duct leading from said accumulator to a bore housing said control valve, and said control valve being movable from a first position at which said inlet, second pressure and accumulator ducts are in fluid communication with each other to a second position at which fluid communication between accululator and pressure ducts.

12. The percussion tool as defined in claim 1 including a control valve between said inlet and second pressure ducts, an accumulator, an accumulator duct leading from said accumulator to a bore housing said control valve, said control valve being movable from a first position at which said inlet, second pressure and accumulator dicts are in fluid communication with each other to a second position at which fluid communication between the accumulator and pressure ducts, said control valve in a second annular open ended valve sleeve, and spring means biasing said second valve sleeve toward its second position.

13. The percussion tool as defined in claim 1 including a control valve between said inlet and second pressure ducts, an accumulator, an accumulator duct leading from said accumulator to a bore housing said control valve, said control valve being movable from a first position at which said inlet, second pressure and accumulator ducts are in fluid communication with each other to a second position at which fluid communication between the accumulator and pressure ducts, said control valve in a second annular open ended valve sleeve, spring means biasing said second valve sleeve toward its second position, said second valve sleeve includes a terminal annular face more adjacent said accumulator and second pressure ducts than said inlet duct, and a plurality of grooves in said terminal annular end face.

14. The percussion tool as defined in claim 2 wherein said valve means has an annular collar on its outer peripheral surface, said collar includes oppositely facing annular surfaces, said control duct opens into said bore for impinging pressurized fluid upon a first of said faces, a duct for placing said bore adjacent a second of said faces in fluid communication with said return duct, and the area of said first face is greater than the area of said second face.

15. The percussion tool as defined in claim 2 including spring means normally biasing said valve sleeve in a direction toward said second position.

16. The percussion tool as defined in claim 2 wherein said first means is a radially outwardly opening circumferential groove in said valve sleeve outer peripheral surface.

17. The percussion tool as defined in claim 2 wherein said piston has a pair of annular axially oppositely facing surfaces of differing surface areas, a larger of said annular surfaces being in fluid communication with said first pressure duct, and a smaller of said annular surfaces being in fluid communication with said second pressure duct.

18. The percussion tool as defined in claim 2 wherein said control duct enters said chamber in the area of said first pressure duct and are remote from said second pressure duct, adjustable trottle means for adjusting the rate of flow from said chamber through said control duct, and said control duct being connected to said return duct.

19. The percussion tool as defined in claim 2 wherein said control duct includes a plurality of branch ducts entering said chamber along axially spaced points in the area of said first pressure duct and more remote from said second pressure duct, the throw of said piston being sufficient to completely cover all of said branch ducts and progressively open the same, adjustable throttle means for adjusting the rate of flow from said chamber through said control duct branches, and said control'duct remote from the branches thereof being connected to said return duct.

20. The percussion tool as defined in claim 3 wherein said control duct enters said chamber in the area of said first pressure duct and more remote from said second pressure duct, adjustable trottle means for adjusting the rate of flow from said chamber through said control duct, and said control duct being connected to said return duct. 

1. A percussion tool comprising a housing defining a chamber within which is reciprocally mounted a piston, first and second pressure ducts in fluid communication with said chamber at respective first and second sides thereof, a control duct in fluid communication with said chamber at said second side of said piston, a return duct in fluid communication with said chamber at a point intermediate the points of entry of said first and second pressure ducts relative to said chamber, an inlet duct for delivering a pressurized fluid to said pressure ducts, and movable valve means for alternately placing said inlet and pressure ducts in fluid communication in a first position of said valve means and placing said first pressure and return ducts in fluid communication in a second position of said valve means while at the same time maintaining fluid communication between said inlet and second pressure ducts and closing communication between said inlet and first pressure ducts, said valve means being an annular open ended valve sleeve mounted for reciprocal motion in a bore, said first and second pressure ducts open into said bore at axially opposite ends thereof, said return duct opens into said bore between the points of entry of said first and second pressure ducts relative to said bore, and said valve sleeve has first means on an outer peripheral surface thereof for placing said first pressure and return ducts in fluid communication in said second position.
 2. The percussion tool as defined in claim 1 wherein said valve sleeve has second means on its outer peripheral surface for moving said valve sleeve from its first to its second position under the impingement of fluid thereagainst, and said control duct opens into said bore for so impinging fluid pressure upon said second means.
 3. The percussion tool as defined in claim 1 wherein said valve means has an annular collar on its outer peripheral surface, said collar includes oppositely facing annular surfaces, said control ducT opens into said bore for impinging pressurized fluid upon a first of said faces, a duct for placing said bore adjacent a second of said faces in fluid communication with said return duct, and the area of said first face is greater than the area of said second face.
 4. The percussion tool as defined in claim 1 including spring means normally biasing said valve sleeve in a direction toward said second position.
 5. The percussion tool as defined in claim 1 wherein said first means is a radially outwardly opening circumferential groove in said valve sleeve outer peripheral surface.
 6. The percussion tool as defined in claim 1 wherein said valve means has an annular collar on its outer peripheral surface, said collar includes oppositely facing annular surfaces, said control duct opens into said bore for impinging pressurized fluid upon a first of said faces, a duct for placing said bore adjacent a second of said faces in fluid communication with said return duct, the area of said first face is greater than the area of said second face, said valve sleeve includes an annular terminal end force at an axial end of said valve sleeve disposed adjacent said second pressure duct, said bore includes an annular seat against which abutts said terminal end face in said first position, and a plurality of grooves in said terminal end face whereby fluid pressure acting between said grooves and annular seat apply a force acting in a direction tending to move said valve sleeve from said first to said second position.
 7. The percussion tool as defined in claim 1 wherein said piston has a pair of annular axially oppositely facing surfaces of differing surface areas, a larger of said annular surfaces being in fluid communication with said first pressure duct, and a smaller of said annular surfaces being in fluid communication with said second pressure duct.
 8. The percussion tool as defined in claim 1 wherein said control duct enters said chamber in the area of said first pressure duct and more remote from said second pressure duct, adjustable throttle means for adjusting the rate of flow from said chamber through said control duct, and said control duct being connected to said return duct.
 9. The percussion tool as defined in claim 1 wherein said control duct includes a plurality of branch ducts entering said chamber along axially spaced points in the area of said first pressure duct and more remote from said second pressure duct, the throw of said piston being sufficient to completely cover all of said branch ducts and progressively open the same, adjustable throttle means for adjusting the rate of flow from said chamber through said control duct branches, and said control duct remote from the branches thereof being connected to said return duct.
 10. The percussion tool as defined in claim 1 including a bore in said piston, a flusing pipe disposed in said bore and being attached to said cylinder, and an annular gap between said bore and flashing pipe.
 11. The percussion tool as defined in claim 1 including a control valve between said inlet and second pressure ducts, an accumulator, an accumulator duct leading from said accumulator to a bore housing said control valve, and said control valve being movable from a first position at which said inlet, second pressure and accumulator ducts are in fluid communication with each other to a second position at which fluid communication between accululator and pressure ducts.
 12. The percussion tool as defined in claim 1 including a control valve between said inlet and second pressure ducts, an accumulator, an accumulator duct leading from said accumulator to a bore housing said control valve, said control valve being movable from a first position at which said inlet, second pressure and accumulator dicts are in fluid communication with each other to a second position at which fluid communication between the accumulator and pressure ducts, said control valve in a second annular open ended valve sleeve, and spring means biasing said secoNd valve sleeve toward its second position.
 13. The percussion tool as defined in claim 1 including a control valve between said inlet and second pressure ducts, an accumulator, an accumulator duct leading from said accumulator to a bore housing said control valve, said control valve being movable from a first position at which said inlet, second pressure and accumulator ducts are in fluid communication with each other to a second position at which fluid communication between the accumulator and pressure ducts, said control valve in a second annular open ended valve sleeve, spring means biasing said second valve sleeve toward its second position, said second valve sleeve includes a terminal annular face more adjacent said accumulator and second pressure ducts than said inlet duct, and a plurality of grooves in said terminal annular end face.
 14. The percussion tool as defined in claim 2 wherein said valve means has an annular collar on its outer peripheral surface, said collar includes oppositely facing annular surfaces, said control duct opens into said bore for impinging pressurized fluid upon a first of said faces, a duct for placing said bore adjacent a second of said faces in fluid communication with said return duct, and the area of said first face is greater than the area of said second face.
 15. The percussion tool as defined in claim 2 including spring means normally biasing said valve sleeve in a direction toward said second position.
 16. The percussion tool as defined in claim 2 wherein said first means is a radially outwardly opening circumferential groove in said valve sleeve outer peripheral surface.
 17. The percussion tool as defined in claim 2 wherein said piston has a pair of annular axially oppositely facing surfaces of differing surface areas, a larger of said annular surfaces being in fluid communication with said first pressure duct, and a smaller of said annular surfaces being in fluid communication with said second pressure duct.
 18. The percussion tool as defined in claim 2 wherein said control duct enters said chamber in the area of said first pressure duct and are remote from said second pressure duct, adjustable trottle means for adjusting the rate of flow from said chamber through said control duct, and said control duct being connected to said return duct.
 19. The percussion tool as defined in claim 2 wherein said control duct includes a plurality of branch ducts entering said chamber along axially spaced points in the area of said first pressure duct and more remote from said second pressure duct, the throw of said piston being sufficient to completely cover all of said branch ducts and progressively open the same, adjustable throttle means for adjusting the rate of flow from said chamber through said control duct branches, and said control duct remote from the branches thereof being connected to said return duct.
 20. The percussion tool as defined in claim 3 wherein said control duct enters said chamber in the area of said first pressure duct and more remote from said second pressure duct, adjustable trottle means for adjusting the rate of flow from said chamber through said control duct, and said control duct being connected to said return duct. 